As an evaporative pattern for casting, an expanded molded article made of a thermoplastic resin has conventionally been used. The expanded molded article has been used, for example, in the following casting method. First, an expanded molded article of a desired shape is coated with a mold wash. Next, the expanded molded article is embedded in sand, and a molten metal is poured onto the expanded molded article embedded in the sand. The expanded molded article is thereby thermally decomposed and replaced with the molten metal. Then, a metal cast can be produced by cooling the molten metal.
As an expanded molded article for an evaporative pattern, for example, an expanded beads molded article made of a styrene resin has been used. However, in use of an expanded styrene resin beads molded article, there has been a problem in that a large amount of soot is produced during thermal decomposition of the molded article. This soot causes contamination on the surface of the resulting metal cast and also causes pinholes to be formed inside the cast. The reason why the soot is produced can be considered because the styrene resin has an aromatic ring. To reduce the amount of soot produced, techniques in which a copolymer of a methacrylic acid ester and a styrene monomer such as styrene or α-methylstyrene is employed as an evaporative pattern (refer to Patent Documents 1 and 2) have been proposed.